Brad,
The VST3 plugin for IK Multimedia’s Miroslav Philharmonik only allows for one note at a time to play (sometimes two) regardless of how many notes are triggered by the MIDI controller. I found this to be the case in both C3 and C4 and on two separate laptops, although the MP2 VST3 plugin is fully polyphonic when used with another Windows VST host product that I own. The VST2 plugin works just fine, so for now that is my workaround so not at all urgent.
Bruce